The present invention relates to a thin film semiconductor device having an active region formed in an amorphous semiconductor layer containing microcrystalline phases.
Conventionally, crystalline silicon has typically been used for the fabrication of semiconductor devices. However, since the use of crystalline silicon requires a single crystal silicon wafer as a substrate, the manufacturing cost thereof is high and complicated manufacturing steps are necessary.
On the other hand, a manufacturing process for a semiconductor device using, for example, glow discharge decomposition of hydrogenated amorphous silicon (a-Si:H) requires simpler manufacturing steps than for a similar semiconductor device using single crystal or polycrystalline silicon, and thus the manufacturing cost can be substantially reduced compared with a crystalline device. Recently, it has become possible to form a film of a-Si:H containing microcrystals of a size on the order of 50 .ANG. to 200 .ANG. by increasing the glow discharge power. Such an a-Si:H film containing microcrystals exhibits a smaller optical absorption coefficient and higher doping efficiency than an ordinary a-Si:H film. Therefore, if such an a-Si:H film is used as a window layer in a solar cell, for example, it would appear that a high performance solar cell might be obtainable. However, it has been found that the output current of a solar cell employing an a-Si:H film containing microcrystals is reduced by carrier trapping in the vicinity of the interface between the layer containing microcrystals and the a-Si:H film due to structural misalignment at the interface.
An object of the present invention is thus to provide a thin film semiconductor device which suffers no misalignment between a semiconductor layer containing a microcrystalline phase and an adjacent layer having no such phase in the vicinity of the interface therebetween, while retaining the merits of a device having a microcrystalline phase.